UNIVERSITY  OF  CALIFORNIA  Agricultural  Experiment  Station 

COLLEGE    OF    AGRICULTURE  E.    W.    HILGARD,    DIRECTOR 

BERKELEY,  CALIFORNIA 


CIRCULAR  No.  11 

(March,  1904.) 


FUMIGATION  PRACTICE. 

By  C.  W.  WOODWORTH. 


There  have  been  so  many  demands  for  information  upon  the  practice 
of  Orchard  Fumigation  that  the  edition  of  Bulletin  No.  122  on  that 
subject  has  been  entirely  exhausted.  The  present  circular,  condensed 
from  that  bulletin,  is  intended  to  furnish  this  information  as  to  the 
details  of  the  process,  with  suggestions  of  possible  improvements. 

All  effective  fumigation  is  done  in  inclosed  spaces,  usually  in  cloth 
tents.  This  is  necessary  on  account  of  the  nature  of  gas,  that  of  dif- 
fusing itself  through  the  air,  which  makes  it  so  efficient  in  reaching 
every  insect  on  the  tree.  Unless  inclosed,  it  would  quickly  become 
diluted  and  fail  to  do  effective  killing. 

The  Canvas. — Common  duck  is  now  uniformly  employed  for  making 
the  larger  tents,  most  of  them  being  made  of  the  eight-ounce  canvas, 
such  as  is  used  for  light  sails.  Six-ounce  drilling  is  often  used  for  the 
smaller  tents.  The  cloth  is  lapped  and  double-sewed  in  the  same 
manner  as  for  tents  or  sails.  The  edge  is  usually  simply  hemmed,  but 
some  bind  it  with  rope.  Whenever  permanent  rings  for  handling  are 
attached,  the  tent  is  reinforced,  but  this  is  a  matter  in  which  there  is 
much  diversity.  The  details  of  the  construction  will  depend  somewhat 
on  the  size  and  kind  of  tent,  and  will  be  referred  to  again,  below. 

After  the  making  of  the  tent,  it  was  formerly  the  practice  to  treat  it  in 
some  manner  to  make  it  gas-tight,  so  as  to  confine  the  gas  better. 
Some  f umigators  still  treat  their  tents.  Four  methods  are  used  for  this 
purpose,  all  of  which  seem  to  give  good  satisfaction. 

The  first  method  is  to  thoroughly  treat  the  tent  with  boiled  linseed 
oil.  It  is  applied  freely  with  a  brush,  and  the  whole  cloth  becomes 
saturated  with  it.  The  tent  must  be  kept  spread  out  until  quite  dry, 
for  the  oil  has  a  great  tendency  to  heat  if  not  exposed  freely  to  the  air, 
and  the  cloth  chars  and  becomes  rotten.  If  properly  done,  the  tent 
remains  strong  and  tight,  and  is  not  too  stiff. 

The  second  method  consists  in  the  use  of  sizing  and  paint.     The 


—  2  — 

sizing  is  applied  in  the  same  manner  as  the  oil,  and  penetrates  the  fiber 
of  the  cloth  in  the  same  way.  As  soon  as  this  coat  is  dry  it  is  followed 
by  another  of  rather  thin  flexible  paint,  ^sometimes  on  both  sides;  the 
result  being  a  perfectly  tight  tent  with  a  very  smooth  surface  and  fully 
as  flexible  as  the  oiled  tent.  The  sizing  protects  the  fiber  of  the  cloth, 
so  there  is  no  danger  of  heating. 

The  third  method  is  the  saturation  of  the  cloth  by  a  decoction  of  the 
chopped-up  leaves  of  the  common  prickly  pear  cactus  ( Opuntia  engel- 
mani).  This  decoction  is  made  by  filling  a  barrel  two-thirds  full  of  the 
chopped  stems,  adding  cold  water  until  the  barrel  is  nearly  full;  then 
letting  it  soak  for  twenty-four  hours,  when  it  is  drawn  off  and  strained, 
and  is  ready  for  use.  This  decoction  is  seldom  used  by  itself,  but  other 
substances  are  added  according  to  the  whim  of  the  person  treating  the 
tents.  Very  generally  a  pigment,  like  yellow  ochre  or  Venetian  red,  is 
added  to  give  more  body  to  the  mixture;  sometimes  glue  is  added  also. 
In  tents  treated  with  the  cactus  decoction,  there  is  some  tendency  to 
become  moldy  when  not  in  use,  to  prevent  which  some  prepare  a  tannin 
solution  to  add  to  the  mixture.  The  decoction  may  be  applied  to  the 
tents  with  a  brush,  but  a  better  way  is  to  soak  them  during  the  night 
in  a  trough  containing  the  mixture.  In  the  morning  they  can  be  raised 
by  means  of  ropes  and  pulleys  and  allowed  to  drain  for  some  time  and 
then  spread  out  to  dry.  Tents  treated  with  this  mixture  are  scarcely 
at  all  stiffened  and  seem  to  be  satisfactorily  tight. 

The  fourth  method  is  to  soak  the  canvas  in  a  solution  of  tannin  until 
it  assumes  a  rich  brown  color.  This  method  does  not  make  the  tent  as 
tight  as  those  described  above,  but  is  quite  as  often  used  as  any. 

The  Bell  Tent. — The  tents  known  as  bell  tents  are  cylindrical  in 
shape,  with  the  top  rounded  over  like  a  dome.  They  are  used  in  con- 
nection with  a  derrick,  by  means  of  which  they  are  placed  upon  and 
lifted  from  trees;  the  derrick  also  supports  the  weight  of  the  tent  while 
it  is  upon  the  tree.  The  bell  tent  was  one  of  the  original  forms  of  tents, 
and  while  mostly  supplanted  by  other  styles,  is  still  used  to  a  consider- 
able extent,  especially  for  very  large  trees.  It  is  the  only  form  of  tent 
now  in  use  where  the  whole  weight  of  the  tent  is  not  carried  by  the  tree, 
and  many  favor  it  for  this  reason. 

The  derrick  used  with  the  bell  tents  at  the  present  time  is  that  used 
with  the  Preble  fumigator,  or  some  modification  of  it.  This  is  shown  in 
Fig.  1.  It  consists  of  a  wagon,  which  supports  a  mast  considerably 
higher  than  the  trees  to  be  fumigated,  and  is  braced  at  the  bottom  with 
stays  that  hold  it  rigidly  in  place.  Across  the  top  of  the  mast  a  yard 
is  fastened  and  braced  with  trusses  extending  from  the  mast.  The 
length  of  the  yard  is  about  a  third  longer  than  the  distance  between  the 
rows  of  trees.     Near  each  end  of  the  yard  are  placed  cross-bars  as  shown 


iii  the  illustration.     The  arrangement  of  the  ropes  can  be  understood 
from  a  study  of  the  figure. 

The  heaviest  rope  is  attached  to  the  top  of  the  tent  with  double 
pulleys.  Along  the  lower  edge,  on  the  four  sides  of  the  tent,  are  fastened 
boards,  generally  of  ordinary  six-inch  fencing,  which  are  called  trail 
boards,  and  from  the  center  of  each  of  these  the  trail  ropes  pass  upward 
and  over  pulleys  attached  to  the  yard  and  ends  of  the  cross-bars.  All 
these  ropes  follow  the  yard  until  near  the  mast,  then  passing  again  over 
pulleys,  they  go  down  to  the  bed  of  the  wagon  and  are  fastened  over 
belaying  pins.  The  trail  ropes  pass  through  thimbles  along  the  side  of 
the  tent  as  well  as  through  the  pulley  at  the  center  of  the  trail,  so  that 
when  the  latter  is  drawn  up  to  the  yard  or  cross-bars,  the  sides  of  the 


FIG.  1.  The  Bell  Tent— Derrick  with  one  tent  nearly  in 
place  on  a  tree,  and  the  other  drawn  up  ready  for 
moving. 

tent  are  gathered  in  three  or  four  places  and  raised  almost  as  high. 
The  only  other  ropes  are  the  guide  lines  attached  to  the  center  of  the 
trails  and  hanging  free.  They  are  of  such  length  as  to  reach  the  ground 
when  the  tent  is  elevated. 

The  manipulation  of  these  tents  can  be  readily  understood  from  a 
study  of  the  engraving.  While  the  tree  is  being  fumigated  the  tent  is 
usually  allowed  to  rest  partly  on  the  tree,  and  not  drawn  up  to  the  yard 
as  shown  in  the  illustration.  Two  persons  can  handle  the  apparatus, 
but  three  or  four  greatly  facilitate  the  work.  The  procedure  in  chang- 
ing the  tent  is  as  follows:  Supposing  that  both  tents  are  upon  the  trees 
and  the  time  has  arrived  to  make  the  change,  the  first  operation  is  to 
pull  on  the  main  rope  attached  to  the  center  of  the  tent  and  raise  this 
as  far  as  it  will  go  easily,  and  then  fasten  the  rope  again  to  the  belaying 


pin.  If  short-handed,  one  tent  is  raised  at  a  time,  but  with  plenty  of 
help  both  go  up  at  the  same  time.  The  trail  ropes  are  next  taken  in 
hand  and  pnlled  all  together,  and  if  this  becomes  difficult,  two  (or  even 
one  at  a  time)  are  pulled  until  the  tent  on  all  sides  is  pulled  up  to  the 
yard  and  cross-bars.  While  this  is  going  on  one  person  (or  perhaps 
more)  is  kept  busy  seeing  that  the  tent  is  clearing  the  tree  properly. 
His  first  business  is  to  see  that  the  edge  with  the  trail  boards  is  not 
caught  inside  of  the  tent;  it  should  slip  up  around  outside  of  it.  Later 
he  will  be  occupied  with  making  the  tent  slip  off  the  projecting  branches. 
He  can  generally  do  this  by  pulling  on  the  guide  lines,  but  on  very 
large  trees  he  may  find  a  light  ladder  necessary.  The  removal  of  the 
tent  would  be  comparatively  easy  but  for  the  Avork  at  the  ropes.  After 
all  the  ropes  are  pulled  tight,  including  the  main  rope,  and  both  tents 
are  against  the  yard,  the  apparatus  is  ready  to  shift  to  the  next  row. 
The  wagon  may  be  pulled  along  by  hand,  or  by  a  horse  hitched  to  the 
end  of  the  tongue.  If  the  ground  is  a  little  uneven,  the  apparatus  can 
be  kept  from  tipping  over  by  steadying  it  with  the  guide  lines.  Arriv- 
ing at  the  proper  position  between  the  next  two  trees,  the  first  thing  is 
to  arrange  the  guide  lines  in  their  places  around  the  tree.  The  trail 
ropes  are  now  released  and  the  tent  is  allowed  to  slowly  descend  upon 
the  tree.  While  this  is  taking  place,  one  or  more  are  busy  with  the 
guide  lines,  pulling  the  trail  boards  this  or  that  way  as  may  be  necessary 
to  clear  the  branches.  If  a  branch  is  particularly  spreading  it  may  be 
necessary  to  use  a  ladder,  forcing  it  within  the  tent  by  hand.  Should 
the  trees  be  very  large  the  branches  will  extend  over  the  wagon,  causing 
much  trouble  in  pulling  the  tent  down  on  that  side.  With  a  small, 
symmetrically  shaped  tree  the  tent  can  be  lowered  rapidly  into  place 
without  any  trouble  whatever.  After  the  trail  ropes  are  all  played  out, 
the  main  rope  is  loosened  and  the  tent  allowed  to  settle  to  the  position 
desired,  and  fastened  there.  There  yet  remains  the  job  of  seeing  that 
the  tent  is  tight  to  the  ground  on  all  sides.  The  trail  boards  are  made 
to  lie  on  the  part  of  the  tent  that  is  on  the  ground,  and  earth  is  thrown 
on  any  part  of  the  edge  of  the  tent  that  does  not  lie  down  well.  When 
both  tents  are  thus  in  position  they  are  ready  for  the  "fumigator,"  or 
man  who  charges  the  generator. 

The  Hoop  Tent. — The  form  most  used  in  this  State  is  the  hoop  tent, 
which  is  a  development  from  the  bell  tent  and  is  of  the  same  general 
shape.  The  hoop  was  first  used  as  a  means  of  keeping  the  mouth  of 
the  bell  tent  open,  but  it  was  soon  discarded  in  favor  of  the  trail  boards. 
It  was,  however,  discovered  that  for  rather  small-sized  tents  the  hoop 
afforded  a  better  means  of  handling  than  did  the  derrick. 

The  hoop  tents  now  in  use  range  from  8  to  14  feet  in  diameter.  They 
are  made  in  the  same  way  as  a  bell  tent,  omitting,  however,  the  arrange- 


K07 


5  — 


ments  for  suspending  them,  and  possessing,  instead,  a  series  of  cloth 
loops  for  attaching  the  hoop,  as  is  shown  in  the  engraving. 

The  hoop  is  usually  made  of  j-inch  gas  pipe;  £-inch  pipe  will  do  for 


FIG.  2.    The  Small  Hoop  Text— Throwing  the  tent  over  a  tree. 

the  smaller  sizes,  but  it  is  too  weak  for  hoops  above  10  feet  in  diameter, 
as  it  bends  too  easily  and  soon  becomes  very  crooked.  To  make  the 
hoop,  pipe  is  coupled  together  until  the  proper  length  is  reached  accord- 


FIG.  3.    The  Small  Hoop  Tent— Palling  down  the  tent. 

ing  to  the  size  desired,  and  then  bent  into  shape.  The  union  is  then 
made  by  inserting  into  the  ends  a  piece  of  iron  rod  a  foot  or  less  in 
length  and  just  small  enough  to  enter  the  pipe.     Holes  are  now  drilled 


—  C5  — 

through  the  pipe  and  rod,  and  rivets  are  inserted,  thus  making  the 
joint  fast.  A  coupling  with  right-  and  left-hand  threads  might  be  used 
instead  of  the  rod  and  rivets. 

The  manipulation  of  a  hoop  tent  varies  according  to  its  size.     When 
the  diameter  of  a  tent  is  not  much  greater  than  the  distance  between 


FIG.  4.    The  Small  Hoop  Tent— Ready  for  the  fumigator. 

the  nearest  branches  of  adjacent  trees,  the  procedure  is  that  illustrated 
in  the  diagram,  Fig.  5,  and  depicted  in  Figs.  2-4. 

To  move  such  a  tent  from  one  tree  to  the  next,  two  men  place  them- 
selves on  opposite  sides  of  it,  grasp  the  hoop  and  raise  the  side  which  is 


\D 


FIG.  5.  Diagram  illustrating  the  method  of  shifting  a  small  hoop  tent  from  one  tree  to  another. 
The  letters  indicate  the  successive  positions  of  the  hoop  as  the  tent  is  first  thrown  off  of  one 
tree  on  to  the  ground,  and  then  is  picked  up  and  put  over  the  next. 

opposite  the  tree  to  which  they  intend  to  move  it;  they  step  sidewise, 
dragging  the  side  that  is  on  the  ground  closer  to  the  trunk,  and  the 
hoop  will  be  in  about  the  position  indicated  by  A  in  the  diagram.  The 
men,  still  holding  the  hoop  as  they  first  grasped  it,  continue  to  raise  the 
free  side  until  it  passes  over  the  top  of  the  tree,  when  it  is  allowed  to 


fall  to  the  ground  between  the  two  trees.  In  falling,  the  hoop  naturally 
moves  away  from  the  tree  from  which  it  came,  so  that  the  cloth  falls 
over  the  edge  of  the  hoop,  as  shown  in  the  diagram.     If  this  does  not 


FIG.  6.  The  Large  Hoop  Tent— Putting  the  tent  on  a  tree.  The  tent 
in  this  case  is  being  lifted  from  the  ground,  and  not  shifted  from 
another  tree. 

occur,  the  tent  is  pulled  into  that  position  in  order  that,  when  the  hoop 
is  raised,  the  center  of  the  tent  will  be  brought  at  once  to  about  the 
center  of  the  top  of  the  tree. 


FIG.  7.    The  Large  Hoop  Tent— Pulling  down  the  canvas  so  that  the 
hoop  will  rest  freely  on  the  ground. 

The  men  now  grasp  the  hoop  again,  as  before,  carry  it. toward  the  tree 
and  lift  up  the  farther  edge,  then  with  one  movement  throw  it  over  the 
tree  to  about  the  position  indicated  by  D.     Often  it  will  go  clear  to  the 


ground  and  needs  no  further  attention.  If  it  stays  at  D,  the  men  pro- 
ceed to  the  point  highest  from  the  ground,  and  pull  on  the  hoop  and 
canvas  until  the   former  rests  easily  on  the  ground.     The  cloth  which 


FIG.  8.    The  Large  Hoop  Tent— Beginning  to  raise  the  tent. 

extends  beyond  the  hoops  forms  a  sufficiently  tight  contact  with  the 
ground  if  the  latter  is  ordinarily  level. 

The  manipulation  of  the  large  hoop-tents    differs   from  that  above 
described,  from  the  fact  that  the  proximity  of  the  trees  makes  it  im- 


FIG 


<).    The  Large  Hoop  Tent— The  tent  almost  off  the  tree. 


practicable  to  lay  the  tent  on  the  ground.     The  procedure  in  this  case  is 
indicated  in  the  accompanying  diagram,  Fig.  10,  and  by  Figs.  6-9. 

It  is  better  to  have  three  men  to  handle  these  tents,  although  two  can 
do  it.     When  working  three,  two  take  hold  in  the  same  way  as  described 


—  9 


above  for  the  small  hoop  tents,  and  the  third  pulls  on  the  side  that  is 
raised  to  the  position  A.  The  latter  then  catches  the  hoop  with  a  fork 
at  the  end  of  a  pole,  and  as  the  others  lift  he  assists  by  pushing.  This 
is  shown  in  Figs.  8  and  9. 

When  the  hoop  has  taken  about  the  position  shown  at  B,  in  Fig.  10, 
or  a  little  past  that  point,  the  two  men  holding  the  sides  of  the  tent 
carry  it  to  the  next  tree  to  the  position  C,  and  then  without  pausing, 
and  while  the  tent  is  full  of  air  and  streaming  out  behind  with  the  aid 
of  momentum  acquired,  the  upper  edge  of  the  hoop  is  forced  over  the 
top  of  the  tree  and  down  on  the  other  side.  Generally  it  is  possible  to 
throw  the  hoop  into  the  position  D,  when  it  can  readily  be  pulled  down 
to  the  ground 

If  there  is  any  trouble  in  pulling  the   cloth   over,   the   third  man, 


FIG.  10.     Diagram  illustrating  the  method  of  shifting  a  large  hoop  tent  from  one  tree  to  another. 
The  letters  indicate  the  successive  positions  of  the  hoop. 

having  tossed  his  pole  to  the  next  tent,  goes  around  to  the  near  side  of 
the  tent  just  moved,  and  as  the  others  pull  on  the  far  side,  shakes  the 
cloth  of  the  tent  away  from  the  tree,  thus  relieving  some  of  the  friction. 
The  weight  of  the  hoop  of  these  large  tents  greatly  helps  in  the  process 
of  slipping  the  cloth  over  the  tree,  the  most  energy  being  required  in 
removing  the  tent,  The  large  tents  are  moved  quite  as  rapidly  as  are 
the  smaller  ones.  It  will  be  noticed  that  the  cloth  is  turned  inside  out 
with  each  change  in  the  case  of  the  larger  tents,  but  with  the  smaller 
ones  the  same  side  of  the  cloth  is  always  next  to  the  tree. 

Method  of  Cutting  Cloth  for  Bell  Tents. — All  of  these  tents  are  made 
in  the  same  manner,  and  are  the  most  economical  in  cloth  of  any  tents 
made.  Commonly  the  tent  is  made  by  the  "cut  and  fit"  method. 
These  tents  may  be  made  with  scarcely  any  loss,  if  cut  according  to  the 
following  directions:  Measure  off  strips  of  a  length  equal  to  twice  the 
height  plus  one  tenth  the  diameter  of  the  tent  desired.     These  will  make 


—  10  — 

two  strips  each  by  marking  the  exact  middle  and  measuring  off  on  one 
edge  from  the  middle  line  one  quarter  of  the  diameter  of  the  tent  and 
on  the  other  one  half  the  diameter.  Now  take  a  long  strip  of  molding 
and  bend  it  so  as  to  touch  these  three  points  and  mark  off  the  curve  so 


luuicc   hcighth   of  tent  plus  /0   the    diAmetc 
* ~k  duinetcr *■ 


FIG.  11.    Method  of  cutting  cloth  for  boll  tents. 

produced.  This  allows  for  the  seam.  In  making  up,  sew  the  two  cut 
edges  together  in  each  pair  of  strips.  The  accompanying  figure  will 
assist  in  making  these  directions  plain. 

The  Box  Tent. — A  recent  development  along  this  line  is  what  is  known 
as  the  box  tent.     It  is  an  Eastern  idea  devised  for  use  on  deciduous 


FIG.  12.    The  Box  Tent— Lifter  in  position  over  a  tent  ready  to 
remove  it  from  the  tree. 

trees,  in  which  the  wood  is  less  pliable  and  more  easily  broken  than  is 
that  of  citrus  trees.  It  may  deserve  a  trial  in  our  orchards,  although, 
doubtless,  we  would  soon  simplify  the  handling  so  as  to  work  more 
rapidly  than  is  now  possible. 

The  box  tent  is  somewhat  intermediate  between  the  bell,  or  hoop  tent, 
and  a  sheet  tent.  It  has  something  of  the  shape  of  the  hoop  tent,  but 
flaring  beneath  and  without  anything  stiff  at  the  bottom.  It  is  made 
with  a  square  top-piece  and  with  four  sides,  which  are  a  half  larger  at 
the  bottom  than  at  the  top. 


—  11  — 

The  manipulation  of  this  tent  is  accomplished  by  the  use  of  a  pole 
called  the  "lifter."  This  pole  has  a  piece  of  scantling  fastened  to  the 
bottom  and  braced,  as  shown  in  Fig.  12,  and  in  the  accompanying 
diagram,  Fig.  13.  To  the  top  of  the  pole  is  attached  a  guy  rope  and  a 
block  pulley,  over  which  passes  a  rope  for  lifting  the  tent.  A  small  Y 
at  a  convenient  height  for  fastening  the  rope  completes  the  lifter. 

In  changing  the  tent  from  one  tree  to  another  the  process  is  to  place 
the  lifter  next  to  the  tree  to  be  uncovered.  The  guy  rope  is  then  tied 
to  an  adjacent  tree  in  such  a  manner  as  to  allow  the  end  of  the  lifter 
to  stand  over  the  center  of  the  tent.  The  end  of  the  lifter  rope  is 
fastened  to  the  edge  of  the  tent  opposite  the  base  of  the  lifter.     As  the 


FIG.  13.  Diagram  illustrating  the  method  of  changing  a  box  tent  from  one  tree  to  another  by 
the  use  of  the  lifter.  A,  B,  C,  D,  and  E  represent  the  successive  positions  of  the  tent;  F,  the 
lifter;  G,  the  guy  rope;  F'  G',  the  second  position  of  lifter  and  guy  rope. 


edge  of  the  tent  is  being  lifted  by  this  rope,  assistants  pull  the  edge  of 
the  tent  aside,  freeing  the  branches;  small  forked  poles  are  used  to  assist 
in  this  work.  After  all  the  branches  are  free  the  tent  is  lowered  to  the 
ground  beside  the  tree. 

The  lifter  is  now  moved  to  the  tree  over  which  the  tent  is  to  be  placed, 
as  shown  at  C.  By  pulling  on  the  lifter  rope,  the  edge  of  the  tent  is 
raised  again  to  the  top  of  the  pole,  when  the  rope  is  fastened.  Two 
persons  now  take  hold  of  the  edges  of  the  tent  and  pull  them  around 
the  tree,  while  a  third  pulls  on  the  guy  rope  until  the  top  of  the  tent  is 
over  the  top  of  the  tree,  when  the  tent  is  lowered  and  pulled  into  posi- 
tion. The  movement  of  the  lifter  by  means  of  the  guy  rope  is  not 
indicated  in  the  drawing,  but  can  be  readily  understood  without.  The 
same  movement  is  useful  in  untenting  a  tree. 

After  letting  the  tent  down  over  the  tree  the  lifter  rope  is  untied  and 
the  bottom  of  the  tent  pushed  up  toward  the  tree  and  made  to  lie  close 


—  12  — 

to  the  ground.     If  necessary,  a  little  earth  is  thrown  upon  it  to  hold  it 
down. 

The  Sheet  Tent. — The  form  that  seems »  most  likely  to  replace  all 
others,  and  has  now  indeed  almost  done  so,  is  the  sheet  tent.  It  is  the 
simplest  to  make,  the  most  readily  adaptable  to  all  sizes  of  trees,  and 


^\. 


A4K 


Iff.  I  ^ 


"\ 


\ 


._;£: 


FIG.  14.    Diagram  illustrating  the  method  of  shifting  a  sheet  tent  from  one  tree  to  another.    The 
letters  represent  the  successive  positions  of  the  end  of  the  pole. 

is  almost  as  readily  moved  from  tree  to  tree  as  the  hoop  tent.  It  con- 
tains, however,  a  great  deal  of  useless  canvas,  which  is  an  objection,  to 
the  economical  mind. 


FIG.  15.    The  Sheet  Tent— Beginning  to  lift  the  edge  of  the  tent. 

Sheet  tents  are  made  either  in  a  regular  or  in  an  oval  hexagon,  and 
perfectly  flat.  A  pair  of  rings  is  often  attached  on  each  side,  near  what 
is  intended  as  the  front  edge;  it  is  convenient  to  attach  these  rings  by 


13 


iron  links,  so  that  they  can  be  rattled  and  found  in  the  dark  by  shaking 
the  tent. 

The  movement  of  the  tent  is  accomplished  by  the  use  of  two  poles. 

^■M|i[^Hi|HAi^H__^^^^_-__-_i^H___-___-i 


FIG.  16.    The  Sheet  Tent— The  tent  partly  over  the  next  tree. 

These  are  usually  simple  poles  with  a  small  rod  projecting  from  the 
upper  end,  over  which  the  ring  of  the  tent  is  slipped;  a  rope  is  also 
fastened  at  the  upper  end.     The  length  of  the  pole  is  slightly  greater 


FIG.  17.    The  Sheet  Tent— Tree  almost  covered,  pole  falling. 

than  the  height  of  the  trees  it  is  desired  to  cover.  Sometimes  the  pole 
has  the  same  shape  as  the  lifter  used  for  the  box  tents,  but  the  pulleys 
and  guy  ropes  are  not  needed,  except  for  the  largest  trees. 


—  14  — 

The  ordinary  process  of  moving  the  sheet  tent  is  shown  in  Figs.  15-18 
and  by  the  accompanying  diagram,  Fig.  14.  A  bird's-eye  view  is  also 
shown  in  Fig.  19.  The  men  approach  the  tent  to  be  moved,  poles  in 
hand,  and  finding  the  rings  insert  the  small  rods  at  the  end  of  the  poles 
and  take  a  hitch  with  the  rope  over  the  ring  to  prevent  the  latter  from 
slipping  off.  They  then  proceed  to  the  other  end  of  their  poles,  which 
they  have  placed  even  with  the  trunk  on  opposite  sides  of  the  tree  to 
which  the  tent  is  to  go.  While  taking  this  station  they  have  not  let  go 
of  the  rope,  but  have  held  it  tight  enough  not  to  loosen  the  tent  ring. 
The  next  step  in  the  process  is  to  place  one  foot  on  the  end  of  the  pole 
to  prevent  it  from  slipping,  and  to  pull  on  the  rope.  This  will  lift  up 
the  edge  of  the  tent  as  shown  at  A  in  Fig.  14.  As  the  men  continue  to 
pull  on  the  rope  the  end  attached  to  the  tent  moves  through  the  arc 


FIG.  18.    The  Sheet  Tent— Adjusting  the  bottom  of  the  tent. 

indicated  by  the  line  of  arrows.  As  soon  as  the  pole  becomes  nearly 
enough  upright  so  as  not  to  slip  when  the  foot  is  removed  from  the  end, 
the  man  backs  off,  away  from  the  tree,  and  thus  gets  a  more  direct  pull 
on  the  tent,  which  by  this  time  has  begun  to  require  some  considerable 
effort.  This  becomes  necessary  also  in  order  that  the  pull  from  each 
side  may  stretch  out  the  front  edge  of  the  tent  so  that  it  may  clear  the 
top  of  the  tree. 

The  tent  is  now  spread  out  over  two  trees  and  reaches  the  ground  on 
either  side.  As  the  men  at  the  ropes  continue  to  back  away  the  tent  is 
slipped  from  one  tree  to  the  next  and  the  poles  fall  to  the  ground.  In 
this  last  stage  in  the  process  care  must  be  taken  that  both  poles  reach  the 
ground  at  about  the  same  time.  If  this  is  not  done  the  tent  will  shift 
to  the  side  of  the  pole  which  first  reaches  the  ground,  and  if  that  side  is 


—  15  — 

pulled  very  much  too  fast  the  tent  may  not  reach  the  ground  on  the 
opposite  side,  and  sheet  tents  are  rather  harder  to  adjust  than  other 
kinds.  This  same  difficulty,  in  regard  to  the  front  and  back  ends  of  the 
tent,  often  occurs  when  using  a  tent  barely  large  enough  for  the  tree.  If 
the  tent  is  pulled  too  slowly  the  poles  will  slip  when  the  tent  is  not  quite 
over,  and  the  front  will  not  reach  the  ground;  and  on  the  other  hand, 
if  it  is  pulled  too  rapidly,  the  tent  will  go  too  far,  and  the  back  end  be 
free  from  the  ground.  The  oval  tent  was  made  to  overcome  this  diffi- 
culty, for  with  it  care  only  need  be  taken  to  slide  the  tent  far  enough. 

When  using  a  large  tent  for  a  very  small  tree  the  tent  is  pulled  up  so 
as  to  have  sufficient  slack  canvas  to  go  over  the  tree,  and  this  is  pulled 
over  by  hand.  When  being  removed,  the  cloth  is  pulled  back  in  the 
same  manner  as  it  was  put  on,  and  dragged  along  the  ground  to  the 
next  tree. 

In  the  case  of  very  large  trees,  which  require  the  lifter  style  of  pole, 
the  process  is  as  follows:  The  poles  are  set  up  and  the  guy  ropes  attached 
as  described  for  the  box  tent,  only  that  two  poles  are  used.  The  other 
ropes  are  now  attached  to  the  tent  at  the  near  edge  and  the  latter  pulled 
to  the  top  of  the  pole.  The  rope  is  then  made  fast,  the  guy  ropes  pulled, 
and  the  tent  slid  in  the  same  manner  as  with  smaller  tents.  Some- 
times the  pole  is  not  set  at  such  an  angle,  but  nearer  the  tent,  when  it 
will  be  necessary,  after  sliding  the  tent  part  of  the  way,  to  again  tie  the 
guy  rope  and  lift  the  bottom  of  the  pole  over;  it  will  then  be  opposite 
the  trunk,  and  the  tent  will  be  lifted  high  enough  when  it  is  given  the 
final  shift. 

When  there  is  fear  of  breaking  the  branches  in  removing  a  tent,  the 
practice  is  to  "  skin  it  off,"  using  a  pole  of  the  lifter  pattern,  and  carry 
the  rope  around  to  the  far  side  and  attach  it  to  the  edge  of  the  tent 
there.  The  tent  by  this  method  slides  over  itself  and  saves  the  tree  to 
that  extent;  it  is  pulled  over  on  to  the  next  tree  as  in  the  preceding 
methods.  Since  much  of  the  tent  by  this  method  falls  to  the  ground,  it 
is  harder  on  the  tree  while  it  is  being  tented.  By  this  process  the  tent 
is  reversed  each  time  it  is  changed. 

Paper  Tents. — Eastern  practice  has  developed  a  number  of  forms  of 
tents  of  fixed  size  with  wooden  frames  covered  with  paper.  These  are 
probably  the  tightest  tents  in  use,  but  are  not  adjustable  to  varying 
sizes  of  trees.  They  are  usually  rectangular  in  shape.  The  frame  is 
made  of  light  wooden  strips  well  braced,  and  the  paper  used  is  ordinary 
building  paper  of  rather  good  quality.  This  is  tacked  on  to  the  frames. 
They  can  only  be  used  for  trees  under  eight  feet  or  thereabouts  in 
height,  except  with  the  use  of  derricks,  which  makes  the  operation 
rather  slow. 

A  form  of  paper  tent  open  on  the  side,  with  a  system  of  clamps  for 


—  16  — 

making  all  tight  after  the  door  is  closed,  is  satisfactory  in  every  way 
except  in  speed. 

One  great  advantage  of  tents  of  this  sort  is  the  uniform  volume,  mak- 
ing the  estimation  of  the  dose  a  matter  to  be  settled  once  for  all,  instead 
of  doing  it  for  each  tree  covered. 

PROCEDURE. 

The  cost  of  fumigation,  and  therefore  the  profit  in  its  use,  depends  in 
a  great  measure  upon  the  arrangement  of  details,  especially  in  the 
economical  use  of  time.  This  is  more  important  than  in  the  case  of 
most  methods  for  killing  insects,  because  of  the  time,  from  forty  to  fifty 
minutes,  required  for  the  operation  of  the  gas.  Fumigation  may  be 
economically  done  in  one  of  two  ways:  with  a  small  outfit  arranged 
to  fit  in  with  other  work,  or  with  a  large  number  of  tents  sufficient  to 
keep  all  hands  busy. 

Work  with  a  small  outfit  can  be  arranged  so  as  to  waste  but  little 
time.  Fortunately,  the  tent  may,  if  desired,  be  left  on  all  night  without 
danger,  so  that  a  strict  record  of  the  time  is  not  necessary,  only  that  it 
be  not  too  short.  A  good  arrangement  is  as  follows:  The  tents  are  placed 
on  at  the  close  of  the  day's  work;  they  are  changed  after  supper,  and 
again  just  before  bedtime,  leaving  them  on  until  morning,  care  being 
taken  to  pull  them  off  before  the  sun  gets  at  them.  This  will  give  three 
fumigations  each  night. 

Large  outfits  are  so  expensive  that  the  owner  generally  feels  like 
keeping  them  in  operation  all  night,  although  some  are  used  only  in  the 
evening.  The  number  of  tents  necessary  will  depend  on  the  size  of  the 
tent  and  the  number  of  men.  The  smallest  number  of  men  that  can 
work  to  advantage  is  two;  they  could  handle  perhaps  twenty  tents  of 
medium  size.  This  would  allow  two  minutes  for  each  tent,  which  ought 
to  be  sufficient  to  change  the  tent  and  introduce  the  chemicals.  It  is 
doubtful,  however,  if  the  fumigator  should  take  part  in  the  vigorous 
physical  work  of  changing  the  tents  where  so  much  depends  on  his 
judgment.  With  the  new  method  of  determining  the  dose,  described 
below,  this  does  not  hold,  and  two-man  outfits  should  be  entirely 
practical. 

The  number  generally  employed  in  a  fumigating  gang  is  four  or  five, 
according  to  the  size  of  the  trees.  One  man  introduces  the  chemicals, 
another  looks  out  for  the  generator  and  measures  the  acid,  and  two  or 
three  handle  the  tents.  Such  a  gang  can  handle  from  thirty  to  forty 
medium-sized  tents  and  cover  from  four  to  six  acres  of  orchard  in  a 
night. 

There  is  much  variation  in  the  detail  of  procedure  in  fumigating;  one 
of  the  best  methods  is  illustrated  in  the  accompanying  diagram,  Fig.  19. 
It  is  intended  to  represent  a  gang  of  four  working  with  sheet  tents  in 


an  orchard  of  rather  small  trees.  Three  trees  are  shown  newly  covered, 
one  tent  in  the  process  of  being  shifted,  and  three  others  ready  to  have 
the  tents  removed.  The  four  dark  spots  indicate  the  position  of  the  men 
at  the  time  the  fumigator  is  about  to  go  under  the  tent,  and  the  lines  of 
arrows  show  the  paths  over  which  the  men  will  travel  during  the  next 
minute.  The  fumigator  enters  the  tent  (Fig.  21),  introduces  the  chem- 
icals and  quickly  withdraws,  sees  that  the  tent  is  down  tightly  to  the 
ground,  and  picks  up  his  tray  of  cyanide  and  proceeds  to  the  next  tree. 
The  helper  holds  up  the  edge  of  the  tent  while  the  fumigator  enters,  and 
drops  it  as  he  comes  out,  then  turning  he  chirps  to  the  horse  in  the  acid 


FIG.  19.  Bird's-eye  view  of  a  young  orchard  being  fumigated  under  sheet  tents.  F,  the  fumi- 
gator; H,  the  helper  who  carries  the  generators  and  measures  the  acid;  R  and  L,  the  tent 
men.    The  arrow  lines  indicate  the  path  traversed  by  each  of  these  parties. 

wagon  and  drives  along  to  the  next  tree.  He  next  removes  the  gen- 
erator from  beneath  this  tree,  pours  out  the  contents  (already  used)  on 
the  ground,  measures  out  the  water  and  then  the  acid  according  to  the 
directions  of  the  fumigator.  (Fig.  20.)  He  then  carries  the  generator 
to  the  fumigator,  who  is  waiting  by  the  next  tent. 

The  tent  men  are  shown  in  diagram  (Fig.  19)  as  they  are  backing  off 
with  the  end  of  the  rope.  They  continue  to  back  off  as  indicated  until 
the  tent  is  over  the  tree,  then  proceeding  to  the  tent  they  adjust  the 
bottom  as  they  pass  around  it,  one  on  either  side.  Proceeding  to  the 
next  tent  they  attach  their  poles,  then  going  to  the  other  end  of  their 
poles,  hold  them  down  with  their  feet  as  they  pull  on  their  ropes  and 


—  18  — 

raise  the  edge  of  the  tent.  As  soon  as  the  pole  is  high  enough  they  back 
off,  and  the  ends  of  the  lines  show  the  position  corresponding  with  that 
they  had  at  first.  The  variations  depend  on  differences  in  the  plan  of 
estimation,  and  in  the  kind  of  tent. 


FIG.  20.  The  Aoid  Wagon— The  helper  in  the  act  of  measuring  the 
acid  in  a  graduate.  A  generator  is  shown  on  the  shelf  below 
the  water  tank.  The  torch  is  shown  above  and  between  the 
acid  and  water  tanks. 


FIG.  21.     The  Fimigator,  in  the  act  of  charging  ;i  generator  under 
the  hoop  tent. 

Estimating  the  Dose. — The  responsibility  in  the  whole  process  rests  on 
the  fumigator,  for  he  is  the  one  who  chooses  the  quantity  of  the  dose;  in 
practice  the  amount  prescribed  has  depended  wholly  upon  his  personal 
judgment.     The  fumigator  looks  at  a  tree  and  says  eight  ounces,  six  and 


—  19  — 

a  half  ounces,  or  ten  ounces,  according  to  his  idea  of  its  size.  The  result 
is  that  a  great  deal  of  unsatisfactory  work  is  done.  The  wonder  is,  that 
the  results  are  as  uniform  as  they  are.  There  are  two  ways  of  verifying 
one's  judgment  as  to  the  proper  doses  to  be  given.  The  one  most  com- 
monly used  is  a  subsequent  inspection  of  the  trees;  the  practice  being 
to  give  a  little  more  gas  than  the  trees  will  stand  without  injury.  If  the 
slight  injury  produced  is  the  same  on  all  the  trees,  the  fumigator's  judg- 
ment is  supposed  to  be  working  normally.  This  is  very  misleading,  for 
the  larger  the  tree  the  greater  the  injury,  if  the  dose  is  properly  propor- 
tional to  the  cubic  content.  The  reason  for  this  is  the  difference  in  the 
generation  of  the  gas  in  large  quantities,  and  its  relatively  sloAver  diffu- 
sion in  a  large  volume. 

The  other  method  is  to  measure  the  tree  and  find  the  amount  of  the  dose 
by  consulting  the  tables.  If  the  tables  are  correctly  calculated  and  the 
measurement  accurately  done,  this  is  a  safe  method;  but  there  are  grave 
difficulties  in  the  way  of  accurately  measuring  a  tree.  If  not  tented,  it  is 
difficult  to  judge  how  much  to  allow  for  the  bending  of  the  branches 
under  the  weight  of  the  tent.  If  tented,  which  is  really  the  correct  way, 
there  are  practical  difficulties  in  measuring  the  diameter  and  height. 
To  simplify  the  measurement  and  estimation  of  a  tent  the  following 
table,  based  upon  volume,  was  prepared  by  the  author.  The  center 
column  gives  the  various  doses  corresponding  to  the  sizes  of  trees  given 
in  the  columns  on  either  side.  Those  on  one  side  have  been  calculated 
so  as  to  give  three  parts  of  hydrocyanic  acid  gas  in  1000  parts  of  air 
(or  0.3  per  cent),  on  the  other  side  two  parts  in  1000  of  air  (or  0.2  per 
cent).  For  winter  treatment  for  deciduous  trees,  0.3  per  cent  gas  is 
suggested,  and  is  nearly  the  strength  recommended  in  the  Eastern 
States  for  the  San  Jose  scale.  One  half  of  this  amount  is  not  far  from 
the  commonest  practice  in  this  State  for  citrus  trees.  The  0.2  per 
cent  gas  is  suggested  for  citrus  trees,  and  agrees  with  the  amounts  used 
by  some  of  the  most  successful  fumigators,  although  others  get  fair 
results  with  scarcely  more  than  half  this  amount. 

The  measurements  to  be  taken  when  using  this  table  are,  (1)  around 
the  tent,  and  (2)  over  the  tent  from  ground  to  ground.  If  these  two 
measurements  are  about  equal,  as  they  will  be  for  many  orange  trees, 
the  number  nearest  the  measurement  is  found  in  the  circumference 
column,  and  the  corresponding  dose  will  be  seen  in  the  center  column. 
If  these  two  measurements  are  not  nearly  the  same,  the  outside  columns 
become  of  use,  for  they  show  for  each  size  how  much  difference  must 
occur  to  make  necessary  a  half  ounce  increase  or  decrease  in  the  dose. 
That  is,  for  each  differential  there  must  be  added  or  deducted  one  half 
ounce  of  cyanide.  For  instance,  if  the  difference  between  the  distance 
over  and  around  the  tree  is  5  feet,  and  the  differential  for  that  circum- 
ference is  3  feet  11  inches,  then  the  dose  must  be  increased  or  dimin- 


—  20  — 

ished  by  a  little  more  than  one  half  ounce;  but  if  that  differential  be 
1  foot,  then  for  each  foot  there  must  be  added  or  subtracted  one  half 
ounce,  or  2-$  ounces  for  the  5  feet. 


Table  Showing  Doses  Suitable  for  Trees  of  Different  Measurements. 


0.3  Per  Cent  Gas. 

0.2  Per 

Jent  Gas. 

1  Ounce 
Differential. 

Circumference  of 
Tree. 

CYANIDE. 

Circumference  of 
Tree. 

£  Ounce 
Differential. 

Ft.      In. 
3        5 

Ft.      In. 
19        1 

Ounces. 
2 

Ft.      In. 

22        1 

Ft.      In. 
3      11 

3 

20        6 

21 

23        7 

3        4 

2        7 

21      11 

3 

25 

2      11 

2        4 

23 

H 

26        4 

2        8 

2        2 

24        1 

4 

27        7 

2        6 

1      11 

25        1 

** 

28        9 

2        4 

1      10 

26 

5 

29      10 

2        2 

1        9 

26      10 

«i 

30        9 

2 

1        8 

27        8 

6 

31        8 

1      10 

1        7 

28        5 

*k 

32        7 

1        9 

1        6 

29        1 

7 

33        4 

1        8 

1        5 

29        9 

n 

34 

1        7 

1        4 

30        4 

8 

34        8 

1        6 

1        3 

31        6 

9 

36        1 

1        5 

1        2 

32        7 

10 

37        5 

1        4 

1        1 

33        8 

11 

38        7 

1        3 

34        8 

12 

39      10 

1        2 

11 

35        7 

13 

40      11 

1        1 

10 

36        6 

14 

41      11 

1        1 

10 

37        5 

15 

42      10 

9 

38        3 

16 

43        9 

11 

9 

39 

17 

44        8 

11 

8 

39        9 

18 

45        7 

10 

8 

40        5 

19 

46        5 

10 

7 

41        2 

20 

47        3 

10 

7 

42        8 

22 

48        9 

9 

7 

43      11 

24 

50        2 

9 

6 

45 

26 

51        6 

8 

6 

46        1 

28 

52        8 

8 

6 

47        2 

30 

54 

7 

5 

48        2 

32 

55        3 

7 

As  an  example,  suppose  a  tree  were  35  feet  around  and  36  feet  over 
the  top,  and  a  person  were  using  the  0.2  per  cent  table:  Running 
down  the  circumference  column  we  find  that  34  feet  8  inches  (the 
nearest  to  35  feet)  requires  8  ounces  and  that  the  differential  is 
1  foot  6  inches,  that  is,  35  feet  requires  a  little  over  8  ounces,  and  the 


—  21  — 

difference  between  the  two  measurements  around  and  over  the  tree,  1 
foot,  is  nearly  enough  to  require  another  half  ounce,  so  that  8-J  ounces 
would  be  about  right.  Suppose,  again,  the  distance  around  a  tree  to  be 
40  feet,  and  that  over  the  top  only  35  feet;  using  the  same  table,  we 
find  opposite  39  feet  10  inches  (the  nearest  to  40  feet)  the  dose  12 
ounces.  But  the  distance  over  the  top  is  5  feet  less,  and  a  less  amount 
of  cyanide  Avill  be  necessary.  We  therefore  use  the  differential  (1  foot 
2  inches)  and  deduct  one  half  ounce  for  each  1  foot  2  inches  difference, 
or  about  2  ounces  altogether.  This  leaves  10  ounces  as  the  correct  dose 
for  this  tree. 

Method  of  Measurement. — In  making  these  measurements  the  method 
which    seems   most  feasible  is  that  used  in  studying  the   fumigation 


FIG.  22. 


dosage  reported  in  Bulletin  No.  152  of  this  Station.  The  apparatus  used 
consisted  of  a  fishing  rod  and  wrire  line.  A  piece  of  electric  drop  light 
insulated  cord  Avas  used  as  the  line.  This  consists  of  a  cable  of  many 
tine  copper  wires  covered  with  thread,  which  gives  greater  flexibility  and 
is  less  liable  to  kink  than  a  simple  wire.  The  line  was  marked  off 
into  one-meter  (39.3  inches)  lengths  by  knots;  the  metric  system  was 
used  because  of  convenience  in  calculation.  The  rod  employed  was  the 
ordinary  jointed  fishing-rod,  which  could  be  disconnected  for  transporta- 
tion and  adjusted  to  different  heights  of  trees.  The  sections  of  the 
rod  were  marked  off  into  centimeters  for  use  in  connection  with  the 
line  in  making  the  measurements. 

The  procedure  in  taking  the  measure  of  a  tent  is  as  follows:     Having 


—  22  — 

first  attached  the  line  at  about  its  middle  to  the  end  of  the  rod,  one  end 
of  the  former  is  made  fast  to  the  tent.  The  most  convenient  way  to 
accomplish  this  was  found  to  be  by  means  of  a  hook,  like  a  fish-hook 
from  which  the  barb  had  been  removed.  v  The  most  convenient  place  of 
attachment  was  at  a  point  one  meter  from  the  ground.  After  attaching 
one  end  of  the  line  to  the  tent  the  rest  of  that  half  is  caused  to  lie  up  to 
and  over  the  center  and  top  of  the  tent  by  means  of  the  rod.  The  one 
making  the  measurement  then  walks  around  to  the  opposite  side  of  the 
tent,  rod  in  hand,  holding  the  line  constantly  in  position  over  the  top. 
The  other  end  of  the  line  is  carried  around  the  tent  at  the  same  time 
and  is  then  drawn  taut,  measuring  the  last  fraction  of  meter  by  means 
of  the  graduations  on  the  lower  joint  of  the  rod.  Adding  now  one 
meter,  the  distance  the  first  end  is  from  the  ground,  we  have  the  meas- 
urement of  the  distance  over  the  top  of  the  tent  from  the  ground  on  one 
side  to  the  ground  on  the  other. 

A  second  measurement  was  then  taken  by  throwing  the  line  off  the 
top  of  the  tent  by  means  of  the  rod  and  holding  it  so  that  as  the  meas- 
urer proceeds  around  the  tent  to  the  point  where  the  line  is  attached  it 
will  encircle  the  tent  at  a  point  about  one  meter  from  the  ground.  The 
end  of  the  rod  is  again  brought  into  requisition  and  the  last  fraction  of 
meter  read  in  centimeters.  Both  measurements  are  thus  made  by  one 
person  in  a  single  trip  around  the  tent. 

These  measurements  should  be  made  with  every  tree,  as  it  seems  to 
be  physically  impossible  to  guess  accurately. 

The  accompanying  diagram  (Fig.  23)  will  enable  one  to  determine 
the  volume  of  a  tent  from  these  measurements  or  from  height  and 
diameter. 

New  Dosage  System. — In  Bulletin  No.  152  was  suggested  a  dosage 
system  corresponding  more  nearly  to  the  actual  practice  than  one 
based  simply  upon  the  volume  of  the  tent.  This  is  one  proportional  to 
the  area  of  the  canvas,  and  is  suggested  because  with  the  tents  now 
mostly  in  use  the  leakage  of  the  gas  is  the  most  important  item.  The 
following  table  will  show  how  much  this  scheme  varies  from  previous 
recommendations : 

Size  of  tent,  in  meters- 
Distance  over  tent 13.73  10.86  8.64  6.87  5.40  4.32  3.39 

Distance  around  the  tent 18.30  14.48  11.52  9.16  7.20  5.76  4.52 

Volume  of  tent,  in  steres 108  56  28  14  7  3.5  1.75 

Dose,  in  ounces — 

By  Morse  schedule 25.6  12.8  6.4  3.2  1.6  .8  .4 

Present  suggestion 12.7  8.9  6.2  4.3  3.1  2.2  1.1 

New  Scheme  of  Measuring. — In  order  to  avoid  the  use  of  tables  or  of 
measuring  apparatus  we  have  suggested  the  marking  of  the  dosage  on 
the  tents.     This  system  consists  in  making  a  series  of  parallel  lines  near 


—  23  — 

two  opposite  edges  of  the  tent,  which  are  so  distanced  from  the  center 
point  that  they  shall  correspond  with  the  dosage  of  a  tree  of  the  average 

Distance  over  top  oj  Tent 


FIG.  23. 


shape.     Upon  these  lines  will  be  placed  numerals  indicating  the  dose, 
the  circumference  in  yards    (paces),   and  the  difference   (that  is,   the 


—  24  — 

amount  the  dose  must  be  varied),  should  the  distance  around  be  more 
or  less  than  the  amount  indicated  for  an  average  tent.  This  plan  would 
permit  the  estimation  of  the  dosage  with  sufficient  rapidity  and  a  fair 
degree  of  accuracy.  If  the  tent  is  not  put  on  the  tree  so  that  its  center 
is  directly  over  the  center  of  the  tree,  the  same  dosage  line  may  not 
touch  the  ground  on  the  two  sides,  but  the  average  of  the  two  will  give 
approximately  the  correct  measurement.  A  lateral  displacement  will 
give  no  trouble  of  using  the  one  indicating  the  highest  dosage,  if  the 
rule  is  followed  when  more  than  one  line  touches  the  ground  on  one 
side.     The  following  table  gives  the  scheme  of  marking  tents: 

Numerals  to  be  marked  on  the  lines. 


Distance  from 
Center  of  Tent. 
Ft.          In. 
2            5 

3 

1 

5 

3 

6 

5 

7 

6 

8 

5 

9 

3 

10 

10 

8 

11 

4 

12    . 

8 

13 

10 

14 

11 

16 

17 

18 

18 

11 

Ounces. 

Paces. 

Difference. 

\ 

3 

.1 

1 

4 

.2 

1* 

5 

.3 

2 

6 

.3 

2i 

7 

.4 

3 

8 

.4 

3^ 

9 

.4 

4 

10 

.4 

*k 

11 

.4 

5 

12 

.4 

6 

13 

.5 

7 

14 

.5 

8 

15 

.5 

9 

16 

.6 

10 

17 

.6 

11 

18 

.6 

12 

19 

.7 

This  whole  series  of  lines  would  not  be  all  placed  on  any  one  tent 
ordinarily,  but  only  those  useful  for  the  given  size  of  tent.  Thus,  for  a 
20-foot  tent  the  lines  corresponding  to  a  dose  of  1^  to  4  ounces  would 
be  useful;  for  a  30-foot  tent,  2\  to  8  ounces,  and  for  a  40-foot  tent,  4  to 
12  ounces  would  be  about  the  range.  The  appearance  of  these  lines  on 
a  tent  is  shown  in  Fig.  24. 

The  use  of  the  tent  will  be  evident  from  the  following  example: 
Suppose  the  lines  on  the  ground  at  the  two  sides  of  a  tree  showed  7  and 
9  ounces,  respectively,  and  the  number  of  steps  around  the  tent  was  17. 
The  correct  dosage  would  be  9  ounces.  The  average  between  7  and  9 
would  have  indicated  8  ounces,  but  the  distance  around  was  two  steps 
more  than  15,  the  number  opposite  the  8  ounces,  and  the  difference 
that  should  be  added  for  each  of  these  is  0.5  of  an  ounce. 

Estimating  the  size  of  the  tree  is  usually  done  by  one  of  three  plans. 
Some  persons  plot  the  orchard  in  the  daytime,  indicating  the  dose  for 
each  tree,  and  fumigating  at  night  in  accordance  with  this  prearranged 
plan.  They  claim,  with  some  show  of  truth,  that  they  are  better 
acquainted  with  the  trees  by  daylight  and  can  more  accurately  estimate 


—  25  — 

their  size.  Others  do  this  at  night,  a  row  at  a  time;  maintaining  that, 
with  practice,  it  can  be  done  with  as  much  accuracy  as  when  done  in 
the  daytime,  and  that  the  danger  of  mistaking  the  rows  is  lessened. 
The  third  plan,  which  seems  the  most  accurate,  and  the  only  one  that 
can  be  recommended,  is  to  make  the  estimate  after  the  tent  is  on  the 
tree.  The  weighing  of  the  cyanide  is  done  at  night  as  a  rule,  but  those 
working  by  the  third  plan  generally  have  it  weighed  in  the  daytime. 
When  the  weighing  is  to  be  done  at  night,  a  base  of  supplies  is  estab- 


/      L  I  «>2/  9 


FIG.  24. 


lished  as  near  the  center  of  the  field  as  possible,  and  the  cyanide  and 
acid,  as  well  as  the  water,  are  dispensed  at  that  point,  the  generators 
being  carried  there  on  trays.  A  generator  tray  is  a  frame  holding  four 
generators  in  a  row,  or  eight  if  stacked  two  deep;  a  person  can  carry 
two  trays,  or  generators  enough  for  sixteen  tents.  After  the  chemicals 
are  ready,  the  "fumigator"  takes  up  his  tray  of  cyanide,  and  the  helper 
two  trays  of  generators,  and  they  proceed  to  tent  after  tent,  leaving  and 
charging  a  generator  at  each  tent.  When  half-way  along  the  row,  the 
helper  drops  a  tray  that  has  been  emptied;  when  he  reaches  the 
other  end,  both  trays  are  empty.  The  generators  are  arranged  on  the 
trays,  as  are  also  the  doses  of  cyanide  on  the  fumigator's  tray,  in  the 
order  of  the  trees.  The  next  work  for  the  fumigator  is  to  estimate 
another  row  of  trees,  and  while  he  is  doing  this,  the  helper  gathers  up 
the  generators  of  the  previous  row.  They  soon  both  arrive  at  the  base 
of  supplies  and  proceed  to  measure  and  weigh  the  chemicals  for  a  row 


—  26  — 

on  the  other  side.     The  details  of  the  third  method  have  already  been 
described. 

When  the  weighing  is  done  in  the  daytime,  the  average  dose  is  com- 
monly weighed  into  each  can  or  bag,  and  a  little  added  or  subtracted 
from  the  dose  as  the  size  of  the  tree  may  indicate.  When  the  trees  are 
very  uniform,  the  dose  thus  varying  but  little,  this  may  do  very  well; 
but  if  the  variation  is  greater,  it  will  be  well  to  have  different  sized 
doses  weighed  out.  When  this  is  done  the  can  or  bag  should  indicate 
clearly  the  amount  of  its  contents  by  its  different  shape  or  character. 
This  method  seems  distinctly  preferable  to  night  weighing. 

Charging. — The  generator  now  universally  used  is  the  ordinary 
earthenware  vessel  or  chamber,  the  cheap  yellow  ware  being  generally 
selected.  Some  use  a  perforated  sheet-lead  cover,  but  generally  no 
cover  is  used.  The  fumigator  places  the  generator  on  the  ground  near 
the  trunk  of  the  tree  and  is  then  ready  to  charge  it,  which  he  accom- 
plishes by  dropping  the  cyanide  into  the  diluted  acid  in  the  generator. 
He  has  the  cyanide  either  in  tin  cans  or  in  small  paper  bags;  in  the 
former  case  he  pours  the  cyanide  into  the  acid,  keeping  the  can,  which 
he  replaces  in  his  tray,  but  in  the  latter  case  breaks  the  bag  and  drops 
it  into  the  acid,  bag  and  all.  Some  fumigators  prefer  to  add  the  acid 
last,  in  which  case  the  helper  brings  the  generator  with  only  water  in 
it,  and  keeps  the  acid  in  a  small  pitcher,  one  for  each  generator.  In 
this  case  the  fumigator  puts  the  cyanide  in  the  generator,  as  before,  and 
then  pours  in  the  acid. 

Poisonous  Nature  of  the  Gas. — All  the  work  of  the  fumigator  under 
the  tent  is  done  at  arm's  length.  There  is  no  poison  more  dangerous 
or  fatal  than  hydrocyanic  acid.  The  danger  from  the  gas  is  greatest  as 
it  is  coming  up  from  the  generator.  This  is  so  well  understood  that 
though  the  gas  has  been  used  for  years  by  a  great  many  people,  we 
have  never  heard  of  an  accident  with  it.  There  seems  to  be  no  inju- 
rious effect  from  breathing  the  diluted  gas  that  fills  the  air  when  the 
tents  are  removed,  even  though  it  may  smell  very  strong  and  one  can 
feel  it  very  plainly  in  his  throat  and  chest.  Working  every  night,  for 
months  at  a  time,  does  not  develop  any  abnormal  symptoms,  so  it  can 
be  safely  said  that,  with  proper  care,  there  is  no  particular  danger  in 
the  use  of  the  gas. 

Inspection. — Wherever  fumigation  is  carefully  done  the  tents  will  be 
thoroughly  inspected  every  day.  To  do  this  the  inspector  goes  beneath 
the  tent  as  it  lies  on  the  ground,  and  any  holes  will  be  at  once  seen  by 
the  light  streaming  through;  these  places  are  marked  and  patches 
applied.  Sometimes  the  patch  is  glued  on,  but  the  usual  and  preferable 
way  is  to  sew  it  on.  Sewing  is  done  by  hand  in  the  same  way  as  sails 
are  mended,  or  sometimes  a  sewing-machine  is  used. 


27 


CONCLUDING    REMARKS. 


The  uniform  testimony  of  those  who  have  used  fumigation  exten- 
sively is  that  by  no  other  means  at  any  cost  can  as  effective  work  be 
done  as  by  proper  fumigation.  It  is  also  true  that  at  no  place  where 
fumigation  has  been  followed  for  years  is  it  believed  that  the  method  is 
eradicative.  Some,  indeed,  think  that  it  would  be  if  universally  used, 
but  those  longest  acquainted  with  the  process  do  not  claim  that  for  it. 
AVhen  it  is  well  done,  the  insects  that  escape  are  far  below  one  per  cent; 
but  with  insects  capable  of  increasing  several  hundred  per  cent  in  a 
single  season,  the  destruction  of  over  ninety-nine  per  cent  is  certainly 
not  a  bad  result. 

The  question  between  fumigation  and  spraying  will  usually  resolve 
itself  into  this:  If  the  interest  of  the  tree  or  crop  demands  a  degree  of 
freedom  from  scale  insects  that  can  not  be  insured  by  one  or  two  spray- 
ings, fumigation  will  be  resorted  to.  The  cost  of  cyanide  has  been 
reduced  about  one  half  since  fumigation  was  begun,  and  if  it  should  be 
reduced  to  about  one  half  of  what  it  is  now,  fumigation  would  probably 
entirely  take  the  place  of  spraying  for  scale  insects  on  all  trees,  as  it 
has  now  done  to  such  an  extent  in  the  case  of  citrus  trees  that  are  so 
difficult  to  spray. 


REPORTS  AND  BULLETINS  AVAILABLE  FOR   DISTRIBUTION. 


REPORTS. 


1896.  Report  of  the  Viticultural  Work  during  the  seasons  1887-93,  with  data  regarding 

the  Vintages  of  1894-95. 

1897.  Resistant  Vines,  their  Selection,  Adaptation,  and  Grafting.     Appendix  to  Viti- 

cultural Report  for  1896. 

1898.  Partial  Report  of  Work  of  Agricultural  Experiment  Station  for  the  years  1895-96 

and  1896-97. 
1900.     Report  of  the  Agricultural  Experiment  Station  for  the  year  1897-98. 
1902.     Report  of  the  Agricultural  Experiment  Station  for  1898-1901. 

BULLETINS. 

No.  121.  The  Conservation  of  Soil  Moisture  and  Economy  in  the  Use  of  Irrigation  Water. 

125.  Australian  Saltbush. 

127.  Bench-Grafting  Resistant  Vines. 

128.  Nature,  Value,  and  Utilization  of  Alkali  Lands. 

129.  Report  of  the  Condition  of  Olive  Culture  in  California. 

131.  The  Phylloxera  of  the  Vine. 

132.  Feeding  of  Farm  Animals. 

133.  Tolerance  of  Alkali  by  Various  Cultures. 

134.  Report  of  Condition  of  Vineyards  in  Portions  of  Santa  Clara  Valley. 

135.  The  Potato-Worm  in  California. 

136.  Erinose  of  the  Vine. 

137.  Pickling  Ripe  and  Green  Olives. 

138.  Citrus  Fruit  Culture. 

139.  Orange  and  Lemon  Rot. 

140.  Lands  of  the  Colorado  Delta  in  Salton  Basin,  and  Supplement. 

141.  Deciduous  Fruits  at  Paso  Robles. 

142.  Grasshoppers  in  California. 

143.  California  Peach-Tree  Borer. 

144.  The  Peach-Worm. 

145.  The  Red  Spider  of  Citrus  Trees. 

146.  New  Methods  of  Grafting  and  Budding  Vines. 

147.  Culture  Work  of  the  Substations. 

148.  Resistant  Vines  and  their  Hybrids. 

149.  California  Sugar  Industry. 

150.  The  Value  of  Oak  Leaves  for  Forage. 

151.  Arsenical  Insecticides. 

152.  Fumigation  Dosage. 

153.  Spraying  with  Distillates. 
1.54.  Sulfur  Sprays  for  Red  Spider. 

155.     Directions  for  Spraying  for  the  Codling-Moth. 

Copies  may  be  had  by  application  to  the  Director  of  the  Experiment 
Station,  Berkeley,  California. 


Printed  at  the  State  Printing  Office,  W.  W.  Shannon,  Superintendent, 


